The constitutional rules that govern how states engage with international law have profound implications for foreign affairs, yet we lack comprehensive data on the choices countries make and their motivations. We draw on an original dataset that covers 108 countries over a nearly 200-year period to map countries’ foreign relations law choices and trace their evolution. We find that legal origins and colonial legacies continue to account for most foreign relations law choices. A small number of models emerged in the nineteenth and early twentieth century in Western Europe, subsequently spread through colonial channels, and usually survived decolonization. Departures from received models are rare and usually associated with major political shifts. Prominent political science accounts that emphasize how states design their foreign relations law strategically to enhance their international credibility or entrench democracy or human rights appear to have limited explanatory power over the bulk of foreign relations law today.

Kevin Cope, Pierre-Hugues Verdier & Mila Versteeg, The Global Evolution of Foreign Relations Law, 116 American Journal of International Law, 1–57 (2022).